1. Field of the Invention
The invention relates to electrical connectors. More particularly, the invention relates to methods and apparatus for electrically coupling electrical conductors through a conductive alloy having a low melting point.
2. State of the Art
The electrical coupling of conductors through a liquid metal is well known in the art. One such well known device is the mercury switch where a pair of conductors are disposed in a glass capsule which is partially filled with liquid mercury. An electrical coupling of the conductors is effected by the liquid mercury when the glass capsule is in the appropriate position and the electrical connection is broken when the capsule is in another position.
More recently, it has been known to use low melting point alloys to effect other types of electrical connections. U.S. Pat. No. 3,622,944 to Tsuchiya et al. discloses an electrical connector using a low melting point alloy consisting essentially of gallium and indium which is liquid at room temperature. Conductors are made of a porous solid material impregnated with the low melting point alloy, or, are made of cadmium, bismuth or lead having interfaces between which the low melting point alloy is precipitated. The connector is useful in miniaturized applications to avoid the need for soldering or high contact pressure. In addition, the connector is useful in lowering contact resistance and in eliminating the need to periodically clean contacts.
In the parent of the instant application, a low melting point conductive alloy is used to couple a conductor to the cathode wall of an electrolytic cell. An external metal conductor strap is mounted a spaced distance from the external steel wall of an electrolytic cell where the steel wall is internally joined to the cathodes of the cell, and the interspace between the external metal conductor strap and the external steel wall is filled with an electrical conductor filler metal alloy. The filler metal may be an alloy that melts and becomes liquid at the normal operating temperature of the cell, or may be chosen so that it remains solid at the normal operating temperature of the cell. Alternatively, the filler metal may be an alloy which does not have a precise melting temperature, but rather a melting range through which the alloy first softens, then forms a semi-liquid "slush," and finally becomes a liquid as the temperature is increased. In the case of an alloy which remains solid during operation of the cell, it may be chosen from a group of alloys which expand when solidified so that the filler metal alloy can be heated and poured into the interspace between the conductor strap and the cell wall wherein it is left to cool and expand, thereby forming a tight mechanical bond. Greater efficiency resulting in power savings is produced due to increased electrical and thermal conductivity between the strap and the cell wall. The conductor strap and the steel wall remain in continuous electrical contact across the entire surface area interface between the external metal conductor strap and the external steel wall of the electrolytic cell. Both the conductor strap and the cell wall beneath the conductor strap are protected from oxidation and corrosion.
The present application seeks to apply the concept of a low melting point conductive alloy coupling to other difficult electrical connections. For example, an electrical coupling of copper to aluminum is often a necessity but is difficult to achieve. Welding, brazing, soldering and explosive bonding techniques are expensive and often unreliable. In addition, rigid electrical bus bar systems often require flexible expansion joints which are expensive and often fail because of problems inherent in their design and use. Bus bar systems are used in industry to carry high currents and/or apply large voltages to machinery where the use of wire conductors is impractical. A bus bar is a relatively large substantially rigid copper or aluminum bar suspended from a ceiling or mounted on a wall. Typically, several parallel bus bars carry electrical current throughout a factory where individual machines tap onto the bus bars to obtain electrical power. The dimensions and routing of the bus bars require that flexible expansion couplings be provided at intervals. These flexible couplings usually take the form either of heavy, many stranded metal cables which are welded, soldered, or bolted to adjacent bus bars, or of multiple layers of copper or aluminum strips which are bolted to adjacent bus bars to make a flexible expansion coupling. These expansion couplings are typically designed to accommodate linear movement of the bus bars, as the expansion and contraction of bus bars is substantially linear. Thus, these and other expansion joints are still subject to the hazards of vibration and seismic shock which are nonlinear. In addition, in connecting machinery to bus bars, circuit breakers, switches, and many other electrical connections are often utilized. These circuit breakers, switches, etc., however, are often difficult to manufacture and are subject to damage by oxidation of metal surfaces and corrosion of electrical contacts. When a circuit breaker or switch is operated with high current, arcing between contacts occurs and often damages the contacts, thereby shortening the useful life of the switch or circuit breaker.